[en] The European Union (EU) stress test is part of the review process which Switzerland initiated immediately after the reactor accident in Japan. As a direct consequence of the accident, the Swiss Federal Nuclear Safety Inspectorate (ENSI) issued three formal orders in which the operators of the Swiss nuclear power plants (NPPs) were required to implement immediate measures and to conduct additional reassessments. The immediate measures comprised the establishment of an external emergency storage facility for the Swiss NPPs, including the necessary plant-specific connections, and back-fittings to provide external injection into the spent fuel pools. The additional reassessments focused on the design of the Swiss NPPs against earthquakes, external flooding and a combination thereof. Investigations on the coolant supply for the safety systems and the spent fuel pool cooling were also requested. ENSI carried out an analysis of the events at Fukushima providing detailed descriptions of the causes, consequences and radiological impacts of the accident. The reports analyse the contributory human and organisational factors, and specify lessons that can be derived from this information. ENSI instructed the Swiss operators to take part in the EU stress test. There was to be particular examination of the robustness of the NPPs in case of impacts beyond the design basis due to earthquakes, external flooding and extreme weather conditions, with consequential loss of power supply and heat sink, and the need for severe accident management actions. ENSI requested further clarification on plant specific issues and produced the National Report which was delivered to the EU Commission. A Country Peer Review Draft Report was drawn up for each country, including a list of issues (open points) for further follow-up by the review team. Eight new open points were identified to further improve the safety of the Swiss NPPs. These open points together with the issues identified in the analysis of the events at Fukushima, are being processed according to their importance and urgency in a Swiss action plan. There was a lack of consistency identified with respect to natural hazards assessments where significant differences exist in national approaches and where difficulties were encountered with beyond design margins and cliff-edge effects assessments. The peer review Board recommends that the Western European Nuclear Safety Regulators Association (WENRA) develop guidance on natural hazards assessments, including earthquake, flooding and extreme weather conditions, as well as on the assessment of margins beyond the design basis and cliff-edge effects. In Switzerland, the periodic safety review is mandatory every 10 years; the risk from external hazards is re-evaluated. ENSI required a re-evaluation of severe weather conditions. A comprehensive research project on external flooding was initiated. The Fukushima disaster highlighted the importance of the containment function as the last barrier to protect the people and the environment against radioactive releases resulting from a nuclear accident. All Swiss NPPs are equipped with special bunkered safety systems designed against extreme external events. ENSI requested a new safety case to demonstrate that the Swiss NPPs have adequate protection against the 10,000-year earthquake and the combination of this earthquake and a 10,000-year flooding. The necessary analyses were submitted by the licence holders. A flood-proof and earthquake-resistant external storage facility is in place at Reitnau since June 2011, in order to strengthen the provision for accident mitigation. It contains various operational resources, in particular mobile motor-driven pumps, mobile emergency power generators, hoses and cables, radiation protection suits, tools, diesel fuel and boration agents. This storage facility is located on top of a hill and is accessible by road or by helicopter. The three independent storage buildings are constructed mainly as underground bunkers which are proof against earthquakes and flooding